The present invention relates to devices that are retained inside a body passage and in one particular application to vascular stents for the repair of arterial dilations known as aneurysms.
As a result of arteriosclerosis, portions of blood vessels may become weakened and extremely dilated. These dilated vessels may be treated by bridging the dilation or weakened extended area using a vascular tubular prosthesis. In this way the diseased portion of the vessel is effectively isolated from the pressure inside blood vessels.
Vascular tubular prostheses may be inserted into the diseased portion of the vessel by surgically opening the vessel and suturing the prosthesis into position. However, it may be preferred to insert the prosthesis from a remote opening, such as the femoral artery, adjacent the groin, using a catheter system. This is because the elimination of the need to open a major body cavity may diminish the potential surgical complications.
Generally it is desirable to insert the prosthesis, using a catheter, in a collapsed or compressed condition and then to expand the prosthesis when in position. One reason for this is that it is desirable to avoid substantially occluding the blood flow during the insertion process. Therefore, by collapsing the prosthesis, the prosthesis may be readily positioned inside the vessel, in some cases without substantially occluding the blood flow.
There are generally two techniques for expanding the prosthesis once it is in position at the location to be repaired. One technique uses a malleable metal prosthesis which has two configurations. One configuration has a relatively smaller diameter and the other has a relatively radially expanded configuration contacting and securing to a neck portion on either side of the diseased vessel region. The prosthesis may be a malleable metal ring which may be expanded by a balloon catheter to set the prosthesis in its expanded diameter, inside the neck portion, proximate to the diseased portion of the vessel.
Another general approach is to use a self-expandable prosthesis which may be compressed against a resilient bias. Once in position, the prosthesis is allowed to resiliently expand into contact with the vessel wall.
While a wide variety of solutions have been proposed to the problem of effectively bypassing diseased tissue, various existing prosthetic device designs may have certain deficiencies. For example, in some cases, the neck portion on either side of the diseased vessel portion may be relatively short. This makes it difficult for prosthetic devices to adequately engage the narrow neck on either side of the aneurysm.
In addition, some of the existing prostheses may cause blockage of the blood flow during insertion, which can have physiologically adverse affects. Still another issue is that many existing prostheses do not adequately seal against the internal surface of a vessel, allowing leakage of blood past the prosthesis into the region between the prosthesis and the weakened blood vessel. The consequences of this type of leakage can be traumatic. In some designs, the device may not be adaptable to non-circular or irregularly shaped neck regions.
Still another issue with some known prostheses is that they may require the hospital to stock a variety of prosthesis sizes for different situations and different patient physiologies. Also some designs may require that the prosthesis be custom fitted for each particular patient.
Another difficulty may arise with regard to accurately positioning the prosthesis once it has been expanded. In some cases inaccurate positioning may be problematic. Similarly, many existing prostheses may be dislodged from their desired position so that they do not effectively accomplish the function of protecting a weakened vessel.
Thus, for these and other reasons, there is a continuing need for enhanced solutions to the problem of repairing diseased vessels and in general to the problem of effectively securing prosthetic devices to the internal walls of body passages.